Answer / pillay

A typical 3 phase motor has 3 sets of windings. Each set of
windings have 2 terminals namely the start and the end of
the winding.During the start the end of of all 3 windings
is joined together through a contactor known as the star
contactor and the 3 phase power supply is applied across the
start terminals of the 3 windings.This windings are actually
designed for the application of 2 different phase voltages
across them.So during start up lower voltage is applied and
so a lower current is drawn. but after a few seconds the
connections are changed through the change over of
contactors to the full voltage across the windings known as
delta connections. This start and change over is done by
timer controlled contactors.

Answer / hiren bhatt

in star connection line voltage of system is decreased to 1
by square root of 3 is equal to 1/1.73 of line voltage,
thats why in starting motor get reduced voltage asper this
ratio and hence star connection help to reduce effect of
dv/dt to the connected load and hence its insulation and
starting current protected

Answer / devi kumar

star resistance have more than delta resistance ex:star have 4 ohms delta 2 Ohms so I=V/R star current =230/4 57.5
Delta current = 230/2 = 115

I hv a question regarding power factor improvement just after transformer. I request you to reply me plzz. thank you sir. My friend has a small unit of fabrication. in his factory the main load is a welding machine, lathe machine, grinding machine. this load is not continuous type. now our electricity board has installed 16 KVA, 11000/433 V transformer for our factory. In the energy meter (trivector meter) at LV side of transformer, i hv seen power factor value of 0.15 only when only 3 KW load was flowing. Further electricity board has suggested to install 4 KVAR capacitor at LV side after energy meter. Now my question is that if we permanantly install and switch on 4 KVAR capacitor after energy meter, during some load on transformer and also without any load on transformer, wht will be the power factor shown in energy meter?i dont want to get any penalty by electricity board, so plz suggest me if i can permanantly install and switch on the 4 kvar capacitor or not at LV side of transformer just after energy meter? Thank you again and awaiting for ur positive reply soon.

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